Indirectly heated tubular cathodes



April 16, 1968 .1. DEBLAY INDIRECTLY HEATED TUBULAR CATHODES Filed Dec. 9, 1965 United States Patent Ofice 3,3 78,71 7 Patented Apr. 16, 1968 3,378,717 INDIRECTLY HEATED TUBULAR CA'lI-IODES Jacques Dcblay, Courbevoie, France, assignor to Compagnie Industrielle Francaise des Tubes Electroniques, Societe Anonyme, Courhevoic, France, a French company Filed Dec. 9, 1965, Ser. No. 512,633 Claims priority, application France, Dec. 30, 1964, 386, Patent 1,430,195 1 Claim. (Cl. 313-337) This invention relates to the cathodes of electron tubes and has specific reference to indirectly heated tubular cathodes, also called equipotential cathodes.

One of the most popular cathode types utilized in the manufacture of electron tubes is the tubular cathode con sisting of a hollow metal tube having a round, oval, rectangular or other cross-sectional contour, according to the type of tube, the outer surface of this tube being coated at least partially with a thermionic emission substance, and of an electric resistance mounted inside this tube for indirectly heating the latter at a temperature sufficient to cause the emission of electrons from said coated surface.

This electric resistance, usually referred to as the heator filament, consists in conventional constructions of one or a plurality of linear elements or strands of a single wire or a bent extruded wire, these elements being coated with an insulating material constituting an electrical insulation for the heater filament of the cathode in which this filament is to be inserted.

In most cases the cathode is held in position by a pair of insulating distance-pieces (for example of mica) supporting the other electrodes of the electron-discharge device, and this cathode is connected by means of a metal strip to the corresponding tube pin embedded in the socket of the device.

Most conveniently the terminal lugs or leads of the heater filament are connected by electrically soldering these lugs or leads to the corresponding pins embedded in the tube socket which are properly bent beforehand so that these lugs or leads extend nearly at right angles to these pins when the soldering operation is carried out. This likewise very conventional procedure ensures a better connection between the lugs and the tube pins and at the same time imparts a greater strength of the heater filament, especially when said leads or lugs have intrinsically a sufiicient mechanical strength, that is, when the diameter of the refractory metal from which they are made approximates the maximum values encountered in the manufacture of these electron tube elements. In the other alternative, that is, in the case of heater filaments operating under a relatively high voltage and receiving therefor a low-intensity current, so that they must have a relatively high resistance and therefore be made from a wire of reduced diameter (of the order of, say, 50p) and even if this wire is coiled up in order to increase its transverse moment of inertia, it will be observed that during the tube operation this filament may collapse. Apart from a definitely characterized defective appearance and from the inherent risk of damage of the insulating coating, the shift resulting from this collapse within the cathode prevents the latter from properly operating and involves the rejection of the tube.

It is the essential object of the present invention to prevent the heater filament from collapsing in a cathode of the type set forth hereinabove by so forming the lower end of a cathode of this character that while the end portions of the heater filament inserted through the upper end of the cathode extend freely through the lower end thereof the intermediate sections of the filament are supported therein, thus reliably supporting the complete filament.

To this end, the lower end of the inner tube of the tubular cathode is pressed symmetrically to half the cathode thickness, this double pressing operation forming a vertical partition in the median plane of the lower end of the cathode tube but only in the central portion of this tube end, in order to create at the bottom of the tube two vertical apertures disposed laterally on either side of said partition and through which the two end portions of the heater filament introduced through the upper end of the tube are inserted, the intermediate portions of this filament being supported by the top of said partition.

In order to afford a clearer understanding of this invention and of the manner in which the same is to be carried out in practice, reference will now be made to the accompanying drawing illustrating diagrammatically by way of example a typical form of embodiment of the invention. In the drawing:

FIGURE 1 is a perspective view of the inner metal tube of a cathode constructed according to the teachings of this invention;

FIGURE 2 is a longitudinal section talcen upon the line II-II of FIGURE 3, showing the cathode with its heater filament;

FIGURE 3 is a cross-section taken upon the line III- III of FIGURE 1.

In this example, the metal tube 1 of the cathode has a rectangular cross-sectional contour, and its lower end 2 is pressed at 3 and 4 from two opposite sides, that is, symmetrically in relation to a longitudinal plane of symmetry of the tube, this double pressing operation thus forming a partition in the median plane of the lower end of the tube but only in the central portion of this end, so as to create two apertures 5 and 6 disposed laterally on either side or at either end of the partition thus formed in the lower portion of the tube.

The cathode tube 1 is held in position in the electron tube by a pair of insulating distance-pieces 7 and 8 and connected according to the conventional method by means of a metal strip 11 to the corresponding tube pin 9 embedded in the tube socket 10.

Mounted within the cathode tube 1 is a heater filament 12 inserted from the top of the tube 1 and having in this example the shape of an M of which the outer sections or arms 13 and 14 extend through the aforesaid apertures 5 and 6 formed in the lower end of tube 1; these sections 13 and 14 are connected through leads 15 and 16 respectively to the corresponding tube pins, to which they are soldered as conventional in the art. The two intermediate sections 17 and 18 of the heater filament bearing with their common bent 19 on the top of said partition 3, 4, are properly supported thereby, thus preventing any detrimental collapse of the filament.

Of course, various detail modifications may be brought to the tubular cathode described hereinabove and illustrated in the drawing by way of example, notably in connection with the shape of the cross-sectional contour of the tubular cathode and also with the general configura- 60 tion of the heater filament to be supported by the pressed lower portion of the tube, without inasmuch departing from the spirit and scope of the invention as set forth in the appended claim.

What I claim is:

1. An indirectly heated tubular cathode comprising a metal tube of which the outer surface is coated at least partially with a thermionic emission substance and a filament bent into several sections, this filament being disposed within said tube, the cathode being characterized 70 in that the lower end of said metal tube is pressed symmettions of said filament being supported by the top of said partition and thus prevented from collapsing.

No references cited.

JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner. 

1. AN INDIRECTLY HEATED TUBULAR CATHODE COMPRISING A METAL TUBE OF WHICH THE OUTER SURFACE IS COATED AT LEAST PARTIALLY WITH A THERMIONIC EMISSION SUBSTANCE AND A FILAMENT BENT INTO SEVERAL SECTIONS, THIS FILAMENT BEING DISPOSED WITHIN SAID TUBE, THE CATHODE BEING CHARACTERIZED IN THAT THE LOWER END OF SAID METAL TUBE IS PRESSED SYMMETRICALLY FROM OPPOSITE SIDES TO HALF THE TUBE THICKNESS, THIS DOUBLE PRESSING OPERATION FORMING A VERTICAL PARTITION IN THE MEDIAN PLANE OF THE LOWER END OF THE CATHODE TUBE BUT ONLY IN THE CENTRAL PORTION OF THIS TUBE END, WHEREBY TWO APERTURES DISPOSED LATERALLY AT EITHER END OF SAID PARTITION ARE CREATED, THE TWO END SECTIONS OF THE HEATER FILAMENT INSERTED FROM THE UPPER END OF THE TUBE EXTENDING THROUGH THESE APERTURES, THE INTERMEDIATE SECTIONS OF SAID FILAMENT BEING SUPPORTED BY THE TOP OF SAID PARTITION AND THUS PREVENTED FROM COLLAPSING. 